Process for oxygen refining of pig iron

ABSTRACT

In the refining of pig iron in a convertor vessel in which oxygen is introduced into the melt by means of one or more tuyeres located in the sidewall of the convertor. Excessive wear of the convertor lining opposite the tuyere is avoided by blowing in a protective fluid which shields the lining from the erosive action of the refining gas and excessive slopping due to oscillations caused by introduction of the refining gas are countered by introduction of fluid opposing the movement of the bath, and pulsed to be out of phase with the bath movement.

United States Patent [1 1 Decker I PROCESS FOR OXYGEN REFINING OF PIG IRON [75] Inventor: Alfred Decker, Embourg, Belgium [73] Assignee: Centre de Recherches I Metallurgiques, Brussels, Belgium [22] Filed: Feb. 21, 1973 [21] Appl. No; 334,340

UNITED STATES PATENTS 3,706,549 l2/l972 Knuppel ..75/60 [451 Feb. 12, 1974 Savard 75/60 Moustier 75/60 [5 7 ABSTRACT In the refining of pig iron in a convertor vessel in which oxygen is introduced into the melt by means of one or more tuyeres located in the sidewall of the convertor. Excessive wear of the converter lining opposite the tuyere is avoided by blowing in a protective fluid which shields the lining from the erosive action of the refining gas and excessive slopping due to oscillations caused by introduction of the refining gas are countered by introduction of fluid opposing the movement of the bath, and pulsed to be out of phase with the bath movement.

7 Claims, No Drawings 1 PROCESS FOR OXYGEN REFINING OF PIG IRON The present invention relates to improvements in the refining of pig iron in a convertor. It applies to refining achieved in part or in whole by means of an oxidizing gas being injected into the convertor through a lateral wall and below the metal bath surface.

It is known that recent advances in convertor refining processes have demonstrated the advantages of effecting at least part of the refining by injecting laterally an oxidizing gas into the metal.

The present invention relates to a process for oxygen refining of pig iron in a convertor with lateral introduction of a refining gas.

it is also known that a satisfactory solution has been found to the problem of refractory lining life in a modified Thomas convertor blown with oxygen by making use of tuyeres comprising two coaxial tubes located in the sidewall of the convertor below the metal bath surface, the central tube being used to convey pure oxygen and the peripheral tube being used to convey a protective fluid which may be either liquid or gaseous.

However, it has been observed that the refractory lining located in the opposite sidewall at the extension of the axis of each of those dual tuyeres often suffered from a more pronounced wear probably due to the oxygen jet discharged by the central tube of said tuyeres. The longitudinal axis of these lateral tuyeres is not always oriented so as to pass through the central longitudinal axis of the convertor; indeed, in particular in order to improve the melting of scrap, it has been found to be to advantage to orient the tuyere longitudinal axis in such manner that it will subtend an acute angle, say of with respect to the convertor diameter passing through the entry point at which said tuyere enters said convertor.

From this wear there ensues an alteration in the cross-sectional contour of this refractory lining, with consequent effect on the course of the refining process due to the resulting irregular contour and in addition this wear results in a limitation in the life of the entire lining which is determined by the life of those particular spots that must be repaired due to excessive wear.

The principalobject of the present invention is to provide a process which avoids these drawbacks.

Another object of the invention is to avoid the disadvantages of side blowing as it is conventionally practiced.

In the process which is the object of the present in vention in which one or more refining tuyeres is located in the lateral convertor wall, there is also an injection of an oxidizing gas constituted wholly or in part of commercially pure oxygen and that simultaneously a protective fluid, liquid or gaseous, will be injected into the convertor in such a manner that the area of said wall which is located at the extension of the axis of the refining tuyeres will be protected from the direct influence of the oxygen jet.

This protection is achieved by generating either a protective fluid screen covering said location or by intersecting and deflecting the refining jet by the stream of injected protective fluid.

The oxidizing gas injection according to the invention is preferably effected by means of known refining tuyeres having two coaxial tubes, of which the central tube is used to convey oxygen and of which the peripheral one is used to convey a liquid or gaseous protective fluid, preferably one with an endothermal reaction, such as a hydrocarbon.

According to the invention, the protective fluid injection means simultaneously utilized with the refining tuyere(s) is located in the lateral wall of the convertor, or it may be located in both the convertor bottom and in the sidewall.

Furthermore, the means for protective fluid injection may also consist of porous components through which a gaseous protective fluid is introduced into the melt.

Depending on the results being sought, the lateral refining gas injection is effected toward the central axis of the convertor or it may be virtually tangential to the wall, or it may assume any of the possible orientations between those two extremes, and at the same time it may be in the horizontal direction, or upwards or downwards from a horizontal plane.

It has been observed, especially when the lateral injections are essentially directed towards the central axis of the convertor, that oscillations may arise in the metal bath, consisting of an alternating bath motion with an amplitude appreciably increasing in the direction of lateral injection. Under certain unfavorable conditions, this motion may lead to spitting of metal out of the convertor mouth.

Another object of the present invention is to provide a process effecting considerable reduction of the effects from this phenomenon.

In this aspect of the invention, a process is provided in which a convertor cast iron refining operation is carried out at least in part by injecting an oxidizing gas toward the convertor center, through the lateral wall of the convertor and below the upper level of the metal bath, and in which the moment an alternating motion arises in the bath, the pressure or the lateral injection rate is modulated at a frequency as close as possible to that of the motion which has occurred but out of phase with that motion, so that the alternating motion will be reduced or eliminated.

The term phase opposition is to be construed so that a maximum of injected gas pressure corresponds to a maximum of metal displacement speed towards the injection tuyere, and that a minimum of injection pressure corresponds to a maximum of displacement speed away from the tuyere (in the same direction as that due to injection). It is not required that the refining gas and the protective fluid be injected simultaneously.

The modulation amplitude and its time dependency must be determined empirically as a function of the acutal metal motions and of the resistance offered this motion in the convertor, as well as of the actual phase shift between the two above mentioned phenomena, to wit, the motion of the bath and that of the injected gas. In this respect it may be desirable to utilize two tuyeres at right angles to one another, or it may be advantageous to provide a slight forward phase shift to the alternating phenomenon imparted to the refining jet with respect to the theoretical opposition moment.

The present invention may be employed not only when the refining is effected by oxygen alone, but also when the refining is by means of a lateral jet of oxidizing gas surrounded by a protective fluid, whether the latter is reducing or not. Furthermore, the protective fluid itself may be supplied at appropriately varied pressures. The pulsing phenomenon that is being generated in this fluid mayor may not occur simultaneously with the one imparted to the oxidizing gas, and it may be of the same frequency or of a different frequency and it need not be in phase with the motion of the oxidizing gas.

I claim:

1. A pneumatic process for refining pig iron which comprises:

injecting an oxidizing gas constituted in whole or in part of commercially pure oxygen into a bath of molten metal contained in a convertor, by means of at least one refining tuyere located in the side wall of said convertor;

and simultaneously injecting a liquid or gaseous protective fluid into the convertor, such that the path taken by said protective fluid intercepts the path taken by said oxidizing gas whereby the wall area of said convertor will be protected from the direct erosive attack of the oxygen introduced through said refining tuyere.

2. A process according to claim 1, wherein the oxidizing gas injection is effected by means of refining tuyeres having two coaxial tubes, of which the central one transmits oxygen and of which the peripheral one transmits a protective fluid in liquid or gaseous form, and preferably of endothermal reaction.

3. A process according to claim 1 in which the protective fluid injection means is located in the sidewall of the convertor.

4. A process according to claim 1, wherein the protective fluid injection is by means of tuyeres.

5. A process according to claim 1, wherein the protective fluid is a gas introduced into the convertor through a porous element in the convertor wall.

6. A process according to claim 4 wherein the protective tuyere is located in the lateral wall of the convertor, and is so positioned that its point of entry into said convertor is diametrically opposite the point of entry of that refining tuyere of which the influence must be checked, the axes of these two tuyeres being so oriented as to be coaxial.

7, A pneumatic refining process for pig iron which comprises injecting an oxidizing gas towards the convertor center through a sidewall of the convertor and below the upper metal bath level, and wherein at the moment an alternating motion occurs in the bath, the lateral injection rate are modulated at a frequency as close as possible to that of the motion which has occurred, but appreciably out of phase with same, so that a reduction or elimination of this alternating motion will be achieved. 

2. A process according to claim 1, wherein the oxidizing gas injection is effected by means of refining tuyeres having two coaxial tubes, of which the central one transmits oxygen and of which the peripheral one transmits a protective fluid in liquid or gaseous form, and preferably of endothermal reaction.
 3. A process according to claim 1 in which the protective fluid injection means is located in the sidewall of the convertor.
 4. A process according to claim 1, wherein the protective fluid injection is by means of tuyeres.
 5. A process according to claim 1, wherein the protective fluid is a gas introduced into the convertor through a porous element in the convertor wall.
 6. A process according to claim 4 wherein the protective tuyere is located in the lateral wall of the convertor, and is so positioned that its point of entry into said convertor is diametrically opposite the point of entry of that refining tuyere of which the influence must be checked, the axes of these two tuyeres being so oriented as to be coaxial.
 7. A pneumatic refining process for pig iron which comprises injecting an oxidizing gas towards the convertor center through a sidewall of the convertor and below the upper metal bath level, and wherein at the moment an alternating motion occurs in the bath, the lateral injection rate are modulated at a frequency as close as possible to that of the motion which has occurred, but appreciably out of phase with same, so that a reduction or elimination of this alternating motion will be achieved. 